1. Field of the Invention
The present invention relates to a trochoidal oil pump which makes it possible to improve the reduction of discharge vibration and noise, and which makes it possible to realize this improvement by means of an extremely simple structure.
2. Description of the Related Art
A pump with a construction in which the addendum part and deddendum part of the inner rotor are formed by circular arcs, the addendum part and deddendum part of the outer rotor are formed by circular arcs that correspond to the circular arc tooth shape of said inner rotor, and the deddendum part of the outer rotor is formed with dimensions that are the same as or greater than the dimensions of the addendum part of said outer rotor, so that the space between the inner rotor and outer rotor is divided into only two spaces, i.e., a space that communicates with the intake port and a space that communicates with the discharge port, is disclosed in Japanese Patent Publication No. 63-47914.
Furthermore, a pump in which circular arc parts are formed in the centers of the top parts of the outward-facing engaging teeth of the drive gear, and rectilinear parts are formed which directly connect the end parts of these circular arc parts and the points of initiation of engagement, so that a large clearance is ensured between the top parts of the inward-facing engaging teeth and the top parts of the outward-facing engaging teeth is ensured in areas other than the area where sealing is require, is disclosed in Japanese Patent Publication No. 5-1397.
In Japanese Patent Publication No. 63-47914, since the tooth shapes of the inner rotor and outer rotor are formed by a combination of simple circular arcs, adjacent volume spaces (cells) between the inner rotor and outer rotor communicate with each other in regions other than the positions of the engagement maximum part and engagement minimum part. Consequently, when the volume space between the rotors in the partition part is at a maximum, this volume space communicates with the intake port in a state in which the volume space is not closed off; accordingly, the back flow of the fluid inside the volume space to the intake port cannot be prevented, so that it is difficult to increase the pump efficiency.
Next, in Japanese Patent Publication No. 5-1397, since sealing parts (P1) that contact the inward-facing engaging teeth of the driven gear, and non-contact rectilinear parts (30b, 30c), are formed in locations on the top parts of the outward-facing engaging teeth of the drive gear, it is actually extremely difficult to ensure a sufficient size of the sealing parts and size of the rectilinear parts in the limited range of these top parts; as a result, the rectilinear parts have an extremely limited small range.
This means that the sealing parts, rectilinear parts and engaging parts are formed in tooth surfaces comprising trochoidal curves, i.e., in tooth surfaces comprising a limited tooth shape silhouette, so that the portions that remain after the sealing parts and engaging parts that are required from the standpoint of function are ensured are formed as the rectilinear parts. Accordingly, the shape range of the rectilinear parts is small, and these parts are merely formed as a structure that eliminates contact of the respective top parts in the range where such contact is not required in the engagement of the drive gear and driven gear. These rectilinear parts are formed on the tooth surfaces of the respective top parts of the outward-facing engaging teeth, and the range of these parts is also small; accordingly, slight gaps are formed which constitute non-contact parts in the engagement of the drive gear and driven gear.
The formation of communicating passages that communicate between the adjacent volume spaces that are formed between the drive gear and driven gear by the rectilinear parts formed on the outward-facing engaging teeth is limited to an extremely small range; in actuality, therefore, the non-contact parts have an extremely small range, and it is difficult to vary the size range of these communicating passages or to ensure a sufficiently large size. Consequently, it is difficult to prevent the generation of noise.
Consequently, in cases where non-contact parts are formed on the outward-facing engaging teeth, if a sufficiently large size is ensured for the engaging parts, the non-contact parts have an extremely small range, so that it is difficult to cause these parts to play the role of communicating passages. Conversely, if the size of the non-contact parts is increased in an attempt to ensure communicating passages, the engaging parts are not sufficiently ensured, so that it becomes difficult to stabilize the rotational driving of the rotors. Thus, it is extremely difficult to simultaneously satisfy the requirements for both communicating passages and engagement, and the communicating passages can be installed in only an extremely limited range. Accordingly, even if the engaging parts are ensured, the communicating passages are narrow and the flow rate is small, so that it is difficult to suppress pump noise to a low level, and to reduce discharge pulsation. The task (technical task, object or the like) that the present invention attempts to accomplish is to improve the reduction of discharge pulsation and noise in a trochoidal oil pump, and the form an extremely simple structure.